Epidemiology of Rural MRSA : Is Livestock Contact a Risk Factor?

The goal of this study is to understand the epidemiology of antibiotic-resistant S. aureus, including methicillin resistant S. aureus (MRSA), outside of the hospital environment. Our objective is to characterize the epidemiology of S. aureus in the rural community, focusing on persons who have contact with livestock. We will achieve this by carrying out two parallel prospective cohort studies in Iowa, examining 1) individuals enrolled in the Agricultural Health Study, including those who raise swine; and 2) a matched population-based group with no livestock exposure. We will partner with the state s microbiological diagnostic laboratories in order to collect isolates from the symptomatic S. aureus infections. Our central hypothesis is that individuals working in close proximity to livestock and poultry are at risk of occupational exposure to MRSA. We further hypothesize that farmers in contact with livestock (swine in particular) will be more likely to be colonized with swine-associated S. aureus strains than are individuals without contact. Finally, we expect to see both typical human strains of S. aureus (including USA300) as well as animal-associated strains (such as ST398) causing infections in Iowans. Our rationale is that successful completion will provide opportunities to institute an early warning system to evaluate emerging S. aureus strains, allowing for potential interventions prior to widespread dissemination in the human population. We will test our central hypothesis and accomplish the objective of this application by pursuing the following specific aims:

1. Establish the prevalence, molecular subtypes, and antibiotic resistance profiles of S. aureus in populations of rural Iowans, and determine risk factors for colonization. We hypothesize that individuals in contact with swine will be more likely to carry MRSA than individuals lacking such exposure; that swine workers will more frequently be colonized with swine-associated strains such as ST398; and that S. aureus isolates collected from livestock farmers will more frequently demonstrate resistance to antibiotics including methicillin and tetracyclines than isolates collected from individuals lacking livestock exposure.
2. Determine the incidence and molecular epidemiology of symptomatic S. aureus infections in rural Iowans. We hypothesize that symptomatic infections will be uncommon in our cohort relative to colonization, and that the majority of such infections will be skin and soft tissue infections. We further hypothesize that the majority of infections in our cohorts and elsewhere in the state will be caused by common strains (including USA300), but that some infections will also be caused by animal-associated strains, including ST398.